This invention relates to molded case circuit breakers of the type for protecting against overload current conditions in electric distribution circuits. More specifically, this invention relates to circuit breakers of the aforementioned type which have a shunt trip mechanism for operation of the circuit breaker to a tripped condition from a remote location.
It has been known to provide circuit breakers of the aforementioned type with a shunt trip apparatus for enabling the breaker to be selectively operated to its tripped condition from a remote location. The shunt trip feature is commonly provided by adding a separate molded case enclosure to the side of an existing molded case circuit breaker, the separate enclosure containing the shunt trip elements such as a solenoid and a lever system which is coupled to the circuit breaker through a handle tie or through openings in the respective side walls of the molded cases. Shunt trip circuit breakers of the narrow width residential or small commercial frame type constructed in this manner occupy two pole spaces on a panelboard to which the circuit breaker is mounted, one space being required for the circuit breaker per se and the second space being required for the shunt trip mechanism. Thus, for each shunt trip breaker device of this type utilized, one pole space for a protected branch circuit is sacrificed. U.S. Pat. Nos. 4,209,761, 3,973,230 and 3,820,046 are examples of shunt trip circuit breakers of the aforementioned type.
The aforementioned related copending application Ser. No. 648,397 filed Sept. 7, 1984 discloses a circuit breaker which utilizes a shape memory effect (SME) alloy element as a current responsive trip mechanism for responding to both high and low current level overload conditions. Such structure replaces separate thermal current sensing and latch structures and may replace magnetic current sensing structures within the circuit breaker, thereby substantially reducing the number of parts, the cost, and the occupied space within the circuit breaker housing. The SME element is also utilized advantageously to eliminate calibration operations of the circuit breaker during manufacture. In accordance with this invention, the SME element is further utilized as a shunt trip mechanism and may be readily incorporated within the same housing as the circuit breaker structure.